<?php
    /**
     * Created by PhpStorm.
     * User: duchao
     * Date: 2018/4/28
     * Time: 11:11
     */
    
    namespace jwt;

    use Exception;
    use \DateTime;
    class JWTSdk
    {
        /**
         * When checking nbf, iat or expiration times,
         * we want to provide some extra leeway time to
         * account for clock skew.
         */
        public static $leeway = 0;
    
        /**
         * Allow the current timestamp to be specified.
         * Useful for fixing a value within unit testing.
         *
         * Will default to PHP time() value if null.
         */
        public static $timestamp = null;
    
        public static $supported_algs = array(
            'HS256' => array('hash_hmac', 'SHA256'),
            'HS512' => array('hash_hmac', 'SHA512'),
            'HS384' => array('hash_hmac', 'SHA384'),
            'RS256' => array('openssl', 'SHA256'),
            'RS384' => array('openssl', 'SHA384'),
            'RS512' => array('openssl', 'SHA512'),
        );
    
        /**
         * Decodes a JWT string into a PHP object.
         *
         * @param string        $jwt            The JWT
         * @param string|array  $key            The key, or map of keys.
         *                                      If the algorithm used is asymmetric, this is the public key
         * @param array         $allowed_algs   List of supported verification algorithms
         *                                      Supported algorithms are 'HS256', 'HS384', 'HS512' and 'RS256'
         *
         * @return object The JWT's payload as a PHP object
         *
         * @throws Exception     Provided JWT was invalid
         * @throws SignatureInvalidException    Provided JWT was invalid because the signature verification failed
         * @throws BeforeValidException         Provided JWT is trying to be used before it's eligible as defined by 'nbf'
         * @throws BeforeValidException         Provided JWT is trying to be used before it's been created as defined by 'iat'
         * @throws ExpiredException             Provided JWT has since expired, as defined by the 'exp' claim
         *
         * @uses jsonDecode
         * @uses urlsafeB64Decode
         */
        public static function decode($jwt, $key, array $allowed_algs = array())
        {
            $timestamp = is_null(static::$timestamp) ? time() : static::$timestamp;
        
            if (empty($key)) {
                throw new Exception('Key may not be empty');
            }
            $tks = explode('.', $jwt);
            if (count($tks) != 3) {
                throw new Exception('Wrong number of segments');
            }
            list($headb64, $bodyb64, $cryptob64) = $tks;
            if (null === ($header = static::jsonDecode(static::urlsafeB64Decode($headb64)))) {
                throw new Exception('Invalid header encoding');
            }
            if (null === $payload = static::jsonDecode(static::urlsafeB64Decode($bodyb64))) {
                throw new Exception('Invalid claims encoding');
            }
            if (false === ($sig = static::urlsafeB64Decode($cryptob64))) {
                throw new Exception('Invalid signature encoding');
            }
            if (empty($header->alg)) {
                throw new Exception('Empty algorithm');
            }
            if (empty(static::$supported_algs[$header->alg])) {
                throw new Exception('Algorithm not supported');
            }
            if (!in_array($header->alg, $allowed_algs)) {
                throw new Exception('Algorithm not allowed');
            }
            if (is_array($key) || $key instanceof \ArrayAccess) {
                if (isset($header->kid)) {
                    if (!isset($key[$header->kid])) {
                        throw new Exception('"kid" invalid, unable to lookup correct key');
                    }
                    $key = $key[$header->kid];
                } else {
                    throw new Exception('"kid" empty, unable to lookup correct key');
                }
            }
        
            // Check the signature
            if (!static::verify("$headb64.$bodyb64", $sig, $key, $header->alg)) {
                throw new Exception('Signature verification failed');
            }
        
            // Check if the nbf if it is defined. This is the time that the
            // token can actually be used. If it's not yet that time, abort.
            if (isset($payload->nbf) && $payload->nbf > ($timestamp + static::$leeway)) {
                throw new Exception(
                    'Cannot handle token prior to ' . date(DateTime::ISO8601, $payload->nbf)
                );
            }
        
            // Check that this token has been created before 'now'. This prevents
            // using tokens that have been created for later use (and haven't
            // correctly used the nbf claim).
            if (isset($payload->iat) && $payload->iat > ($timestamp + static::$leeway)) {
                throw new Exception(
                    'Cannot handle token prior to ' . date(DateTime::ISO8601, $payload->iat)
                );
            }
        
            // Check if this token has expired.
            if (isset($payload->exp) && ($timestamp - static::$leeway) >= $payload->exp) {
                throw new Exception('Expired token');
            }
        
            return $payload;
        }
    
    
        public static function encode($payload, $key, $alg = 'HS256', $keyId = null, $head = null)
        {
            $header = array('typ' => 'JWT', 'alg' => $alg);
            if ($keyId !== null) {
                $header['kid'] = $keyId;
            }
            if ( isset($head) && is_array($head) ) {
                $header = array_merge($head, $header);
            }
            $segments = array();
            $segments[] = static::urlsafeB64Encode(static::jsonEncode($header));
            $segments[] = static::urlsafeB64Encode(static::jsonEncode($payload));
            $signing_input = implode('.', $segments);
        
            $signature = static::sign($signing_input, $key, $alg);
            $segments[] = static::urlsafeB64Encode($signature);
        
            return implode('.', $segments);
        }
    
        /**
         * Sign a string with a given key and algorithm.
         *
         * @param string            $msg    The message to sign
         * @param string|resource   $key    The secret key
         * @param string            $alg    The signing algorithm.
         *                                  Supported algorithms are 'HS256', 'HS384', 'HS512' and 'RS256'
         *
         * @return string An encrypted message
         *
         * @throws Exception Unsupported algorithm was specified
         */
        public static function sign($msg, $key, $alg = 'HS256')
        {
            if (empty(static::$supported_algs[$alg])) {
                throw new Exception('Algorithm not supported');
            }
            list($function, $algorithm) = static::$supported_algs[$alg];
            switch($function) {
                case 'hash_hmac':
                    return hash_hmac($algorithm, $msg, $key, true);
                case 'openssl':
                    $signature = '';
                    $success = openssl_sign($msg, $signature, $key, $algorithm);
                    if (!$success) {
                        throw new Exception("OpenSSL unable to sign data");
                    } else {
                        return $signature;
                    }
            }
        }
    
        /**
         * Verify a signature with the message, key and method. Not all methods
         * are symmetric, so we must have a separate verify and sign method.
         *
         * @param string            $msg        The original message (header and body)
         * @param string            $signature  The original signature
         * @param string|resource   $key        For HS*, a string key works. for RS*, must be a resource of an openssl public key
         * @param string            $alg        The algorithm
         *
         * @return bool
         *
         * @throws Exception Invalid Algorithm or OpenSSL failure
         */
        private static function verify($msg, $signature, $key, $alg)
        {
            if (empty(static::$supported_algs[$alg])) {
                throw new Exception('Algorithm not supported');
            }
        
            list($function, $algorithm) = static::$supported_algs[$alg];
            switch($function) {
                case 'openssl':
                    $success = openssl_verify($msg, $signature, $key, $algorithm);
                    if ($success === 1) {
                        return true;
                    } elseif ($success === 0) {
                        return false;
                    }
                    // returns 1 on success, 0 on failure, -1 on error.
                    throw new Exception(
                        'OpenSSL error: ' . openssl_error_string()
                    );
                case 'hash_hmac':
                default:
                    $hash = hash_hmac($algorithm, $msg, $key, true);
                    if (function_exists('hash_equals')) {
                        return hash_equals($signature, $hash);
                    }
                    $len = min(static::safeStrlen($signature), static::safeStrlen($hash));
                
                    $status = 0;
                    for ($i = 0; $i < $len; $i++) {
                        $status |= (ord($signature[$i]) ^ ord($hash[$i]));
                    }
                    $status |= (static::safeStrlen($signature) ^ static::safeStrlen($hash));
                
                    return ($status === 0);
            }
        }
    
        /**
         * Decode a JSON string into a PHP object.
         *
         * @param string $input JSON string
         *
         * @return object Object representation of JSON string
         *
         * @throws Exception Provided string was invalid JSON
         */
        public static function jsonDecode($input)
        {
            if (version_compare(PHP_VERSION, '5.4.0', '>=') && !(defined('JSON_C_VERSION') && PHP_INT_SIZE > 4)) {
                /** In PHP >=5.4.0, json_decode() accepts an options parameter, that allows you
                 * to specify that large ints (like Steam Transaction IDs) should be treated as
                 * strings, rather than the PHP default behaviour of converting them to floats.
                 */
                $obj = json_decode($input, false, 512, JSON_BIGINT_AS_STRING);
            } else {
                /** Not all servers will support that, however, so for older versions we must
                 * manually detect large ints in the JSON string and quote them (thus converting
                 *them to strings) before decoding, hence the preg_replace() call.
                 */
                $max_int_length = strlen((string) PHP_INT_MAX) - 1;
                $json_without_bigints = preg_replace('/:\s*(-?\d{'.$max_int_length.',})/', ': "$1"', $input);
                $obj = json_decode($json_without_bigints);
            }
        
            if (function_exists('json_last_error') && $errno = json_last_error()) {
                static::handleJsonError($errno);
            } elseif ($obj === null && $input !== 'null') {
                throw new Exception('Null result with non-null input');
            }
            return $obj;
        }
    
        /**
         * Encode a PHP object into a JSON string.
         *
         * @param object|array $input A PHP object or array
         *
         * @return string JSON representation of the PHP object or array
         *
         * @throws Exception Provided object could not be encoded to valid JSON
         */
        public static function jsonEncode($input)
        {
            $json = json_encode($input);
            if (function_exists('json_last_error') && $errno = json_last_error()) {
                static::handleJsonError($errno);
            } elseif ($json === 'null' && $input !== null) {
                throw new Exception('Null result with non-null input');
            }
            return $json;
        }
    
        /**
         * Decode a string with URL-safe Base64.
         *
         * @param string $input A Base64 encoded string
         *
         * @return string A decoded string
         */
        public static function urlsafeB64Decode($input)
        {
            $remainder = strlen($input) % 4;
            if ($remainder) {
                $padlen = 4 - $remainder;
                $input .= str_repeat('=', $padlen);
            }
            return base64_decode(strtr($input, '-_', '+/'));
        }
    
        /**
         * Encode a string with URL-safe Base64.
         *
         * @param string $input The string you want encoded
         *
         * @return string The base64 encode of what you passed in
         */
        public static function urlsafeB64Encode($input)
        {
            return str_replace('=', '', strtr(base64_encode($input), '+/', '-_'));
        }
    
    
        private static function handleJsonError($errno)
        {
            $messages = array(
                JSON_ERROR_DEPTH => 'Maximum stack depth exceeded',
                JSON_ERROR_STATE_MISMATCH => 'Invalid or malformed JSON',
                JSON_ERROR_CTRL_CHAR => 'Unexpected control character found',
                JSON_ERROR_SYNTAX => 'Syntax error, malformed JSON',
                JSON_ERROR_UTF8 => 'Malformed UTF-8 characters' //PHP >= 5.3.3
            );
            throw new Exception(
                isset($messages[$errno])
                    ? $messages[$errno]
                    : 'Unknown JSON error: ' . $errno
            );
        }
    
        /**
         * Get the number of bytes in cryptographic strings.
         *
         * @param string
         *
         * @return int
         */
        private static function safeStrlen($str)
        {
            if (function_exists('mb_strlen')) {
                return mb_strlen($str, '8bit');
            }
            return strlen($str);
        }
    }